Effect of AM colonization on growth and yield in potato
This thesis aims to investigate the effect AM fungal inoculation and subsequent colonisation on the growth and tuber yield of potato. Different AM fungal inocula used produced different responses. Some fungal inocula did not colonise potato roots at all, even in suitable growth substrates (i.e. Glomus fasiculatum). It was observed that Glomus mosseae and Vaminoc Tâ formed the best associations with potato. However, the viability of inocula is a major concern for their commercial use. Phosphate had a significant effect on the growth of potato and AM formation. Plants grown in low phosphate were smaller in size and produced lower numbers of market sized tubers. Mycorrhizal formation was promoted at low P soil concentrations. Mycorrhizal plants grown at low P had increased yields of market sized tubers and tuber weights compared to the NM plants. This was mainly due to improved P nutrition and resulted in a tuber yield comparable to that produced by plants grown in high P. Increasing soil P concentrations decreased the level of AM formation. If mycorrhizal plants were given high P or grown at a low light intensity then no beneficial effects of colonisation were seen. Plants grown at low light intensities could not cope with the increased below ground demand of tubers and AM and this resulted in a decrease in the shoot C concentration. Early tuber removal decreased C-assimilation, increased subsequent tuber number and decreased the level of AM formation. This indicated that potato plants need to maintain a high photosynthetic rate in order to maintain an AM association. A decrease in C-assimilation caused a decrease in AM formation. The formation of AM in different potato cultivars was investigated. It was shown that different cultivars had varying responses to AM fungal inoculation. Those cultivars that had low disease resistance to microbial pathogens had higher levels of AM colonisation. Correlation analysis showed that there was an inverse relationship between disease resistance, and AM colonisation, irrespective of the growth of the potato. This indicated that breeding for disease resistance may have bred against the formation of AM in potato.